The electron-lattice spin-orbit (SO) coupling in many superconductors of current interest, in particular, the heavy-fermion compounds, is strong compared with the Zeeman energy and the energy scales associated with
superconductivity, and one can call into question the validity of the assumption
that the effective Zeeman interaction in the Bloch bands has the same simple form \(\hat{H}_Z=\mu _B {H} \hat{\sigma }\)  as for bare electrons (here the spin magnetic moment is equal to \(-\mu _B\hat{\sigma }\) ,
\(\mu _B\)  is the Bohr magneton,
the electron charge is \(-e\) , the Landé factor is set to 2, and \(\hat{\sigma }\)  are the Pauli matrices). Even in the presence of the SO coupling,
the Bloch bands in a centrosymmetric crystal are twofold degenerate.[1]} Focusing on just one band, one can write the effective Zeeman Hamiltonian at the wave vector
\( {k} \)  in the general form as \(\hat{H}_Z=-\hat{m}( {k} ) {H} \) , where the Hermitian \(2\times 2\)  matrix \(\hat{m}\)  has the meaning of the magnetic moment of the band electrons.[2]}, [3]}, [4]}
